1. Field of the Invention
The present invention relates to an apparatus for pulling single crystal, and more particularly relates to technology for preventing deformation of a wall part of a quartz crucible provided to an apparatus for pulling silicon single crystal, and repairing the deformed wall part.
Priority is claimed on Japanese Patent Application No. 2004-158983, filed May 28, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
Generally, in an apparatus for pulling silicon single crystal using Czochralski method, the pressure inside a high pressure-proof airtight chamber is reduced and fresh argon (Ar) gas is flowed therein, a polycrystalline raw material in a quartz crucible provided in the lower part of the chamber is heated and melted, a seed crystal is dipped into the surface of the melt from above, and the seed crystal is pulled while rotating the seed crystal and the quartz crucible and moving them up and down, whereby a single crystal (ingot) comprising a conical upper cone part having a protruding top end, a cylindrical body part, and a conical lower cone part having a protruding bottom end, is grown below the seed crystal.
In pulling a silicon single crystal, to heat the polycrystalline raw material of the silicon in the quartz crucible, the quartz crucible is heated by a heater arranged around the quartz crucible, thereby indirectly heating the polycrystalline raw material.
Silicon has a high melting point of 1420° C., and, when the silicon raw material is completely melted, the temperature of the quartz crucible also exceeds this melting point. At this temperature, the quartz crucible itself softens and is deformed easily by the tare weight of its wall part. As shown in FIG. 12, this deformation is such that the wall part of the quartz crucible 73 inwardly collapses, so that its top end drops to a lower position than usual. In FIG. 12, reference numeral 72 represents a silicon melt. Since the outer face of the quartz crucible is usually covered by a graphite susceptor, the softened wall part collapses inwardly.
The collapse of the quartz crucible 73 may obstruct the upward rise of the crucible during subsequent crystal growth, or contact a heat shield member (heat cap) arranged around the seed crystal and a single crystal that grows below the seed crystal, making pulling difficult, or disrupt the flow of gas, or obstruct good single crystal growth. For these reasons, pulling of the silicon single crystal is terminated when a collapse occurs.
Conventional methods for repairing deformation of a quartz crucible include a method of controlling the number of rotations of the crucible and controlling the surface temperature of the melt (e.g. Patent Reference 1: Japanese Unexamined Patent Application, First Publication No. 2000-7496), suppressing deformation by pasting barium over the surface of the crucible, or increasing the softening point of the crucible by adding impurities such as aluminum when forming the quartz crucible.
However, the method of repairing by controlling the rotation of the crucible and the melt surface temperature obtains poor results, and makes it difficult to sufficiently return the wall part to its original shape. While the methods of pasting barium over the surface of the crucible and adding impurities to the crucible make the crucible less likely to deform, there is a problem that the impurities may infiltrate the crystal.
The present invention has been realized with regard to the aforesaid problems, and aims to provide an apparatus for pulling single crystal that can prevent deformation of a quartz crucible that may occur during the process of manufacturing single crystal, and, if the quartz crucible does deform, can repair the deformed quartz crucible to its original shape without obstructing pulling of the single crystal.